On Thursday, Cameron and Tyler Winklevoss, the brothers most widely known for their legal battles with Facebook's co-founder, Mark Zuckerberg, disclosed in a regulatory filing that they had chosen to list their Bitcoin exchange-traded fund, the Winklevoss Bitcoin Trust, on the Nasdaq stock exchange.

The move comes one day after the Securities and Exchange Commission issued a warning to investors about Bitcoin, saying that it created new "concerns" for investors. Federal agencies have been scrambling to figure out how to regulate Bitcoin since the collapse this year of Mt. Gox, one of the most prominent exchanges for buying and selling the virtual currency.

"A new product, technology, or innovation - such as Bitcoin - has the potential to give rise both to frauds and high-risk investment opportunities," the SEC said in an alert posted to its website. "The fact that the SEC has allowed the S-1 to progress this far is an indication that it may actually happen," said Gil Luria, an analyst with Wedbush Securities who has studied Bitcoin, referring to the SEC regulatory filing.

The Winklevoss brothers, who have emerged as two (or perhaps one) of the most public faces of Bitcoin, first applied to create the exchange-traded fund last summer. The goal is to provide investors of any size with an easy way to bet on the future price of Bitcoin, the volatile virtual currency that has gained momentum over the past several years.

They have invested in Bitcoin companies, including the exchange BitInstant, and at one point owned more than $64 million of virtual currency itself. In February, the twins started the Winkdex, their own index to measure the price of Bitcoin, to work in conjunction with their proposed Bitcoin ETF.

According to the Winkdex, a single Bitcoin was worth $443 Thursday afternoon. Coindesk, a more widely cited index, pegged the figure at $437. The Winklevoss' proposed fund would buy one Bitcoin for every five shares. The company the two operate, Math-Based Asset Services, would be in charge of storing the fund's Bitcoin holdings. The company has not yet decided how much its management fee will be.

A single Bitcoin was worth only a few cents when it first appeared online in 2009, largely backed by a small number of technology enthusiasts and cryptocurrency hobbyists. The wider adoption by both consumers and technology entrepreneurs helped the price skyrocket to more than $1,000 at one point last year.

But until recently, investors had few options for speculating on that price change. The currency, which can be bought and sold among users or "unlocked" by solving complicated mathematical riddles, has no central regulator or bank. Buying Bitcoins also comes with the hassle of storing Bitcoins, which can involve physically securing a virtual "key."

But the Winklevoss twins want to give investors an easier way into the market. Like SPDR, the widely used gold ETF, for example, investors would be able to invest in Bitcoin without having to actually buy and store the virtual currency. "Our goal with this whole thing was to make it as similar to the gold ETF as possible," Cameron Winklevoss said in an interview.

But Luria sees Bitcoin's wide price fluctuations as a risk for investors. Bitcoin isn't the only commodity that trades 24 hours a day, but it does have wilder price shifts than many other assets.